Polymer blends are a route to novel and useful materials having improved properties, such as easier processing, better mechanical properties, chemical resistance and lower cost. When two polymers are blended, however, owing to their usually inherent incompatibility, their blend physical properties may be poor. It is desirable and often necessary to add a third constituent, called a compatibilizer, whose purpose it is to improve the blend properties. (D. R. Paul and S. Newman, eds., Polymer Blends, Vols. 1-2, New York, Academic Press, 1978.; N. G. Gaylord, J. Macromol. Sci. Chem., A26(8), 1211 (1989).) Compatibilizers are typically either random, graft, or block copolymers. Reference is also made to U.S. Pat. Nos. 4,885,334 and 4,886,126 for compositions of this general type.
For example, it is known to use a compatibilizer in admixture with a blend of a polyphenylene oxide polymer and a styrene acrylonitrile polymer. The compatibilizer is a block copolymer of styrene and acrylonitrile. Reference is made to U.S. Pat. No. 4,866,126. Block copolymer compatibilizers for a blend of polyphenylene oxides and a "polar thermoplastic resin", which can be a polyester, are described in U.S. Pat. No. 4,885,334. The compatibilizer is a modified block copolymer obtained by subjecting a hydrogenated block copolymer comprising an aromatic vinyl compound polymer block (e.g. derived from styrene) and a conjugated diene compound polymer block (e.g. 1,3, butadiene) to graft polymerization in the presence of a monomer having an epoxy group (e.g. glycidyl methacrylate).
Compatible blends of poly(2,6-dimethyl-1,4-phenylene oxide), with polyesters, having improved impact strength and solvent resistance have been reported previously. Improved tensile properties strength, moldability, flexural modulus, compounding, and smoothness have also been reported.
We have found that blends of certain polyesters with phenylene oxide containing polymers have brittle mechanical properties. Thus, it would be desirable to have a compatibilizer that, when added to these blends, improves their mechanical properties and allows the potential advantages of these blends--e.g., easier processing than phenylene oxide containing polymers, higher thermal dimensional stability than the polyesters alone, and lower cost than phenylene oxide containing polymers--to be realized.